Electrical connection for high energy igniters, and method for producing same



April 15, 1958 2,831,138

EL ELECTRICAL CONNECTION FOR HIGH ENERGY IGNITERS, AND METHODFOR'PRODUCING SAME Filed Feb. 3, 1955 FEE. I

R ICHARD C. TEASEL BY vdgum ATTORNEYS ELECTRICAL CONNECTION FOR HIGHENERGY IGNITERS, AND METHOD FOR PRODUCING SAME Richard C. Tease],Toledo, Ohio, assignor to Champion Spark Plug Company, Toledo, Ohio, acorporation of Delaware Application February 3, 1955, Serial No. 485,842

5 Claims. (Cl. 313-130) This invention relates to an electricalconnection for high energy igniters, and to a method for producing same.

A recent development in the field of spark plugs and jet engine igniterscontemplates a high energy spark discharge over the surface of the noseof a spark plug or igniter. Although many advantages are achieved fromusing this type of discharge to fire reciprocating engines and jetengines, there are also difiiculties. When a high voltage is applied tocause the spark, serious problems are encountered in insulating theignition system. When only a low voltage is applied the discharge mustbe along some semi-conducting surface, but substantial difficulties havebeen encountered in the production of igniters of this type. One majorproblem that has been encountered is the relatively rapid increase inminimum sparking voltage which occurs during use of the igniter. Theterm minimum sparking voltage is used herein to refer to the lowestvoltage applied across the terminals of an igniter that is capable ofcausing a spark discharge across the semi-conductive surface. When ahigh energy, low voltage, igniter is in service in a reciprocatingengine or in a jet engine, the useful life thereof is ended when theminimum sparking voltage exceeds the voltage available in the ignitionsystem, usually between 1000 and 2000 volts. Therefore, the relativelyrapid increase in minimum sparking voltage of high energy igniters canbe, and frequently is, the limiting factor on useful life thereof.

The instant invention is based upon the discovery of an electricalconnection in a high energy igniter, and of a method for producing suchelectrical connection, which substantially prolongs the service lifethereof prior to the increase of minimum sparking voltage to anypredetermined maximum. Such electrical connection is between a centerelectrode of an igniter and a semi-conducting sparking surface, and alsobetween a ground electrode and such surface.

It is, therefore, an object of the invention to provide an improvedelectrical connection in a high energy igniter.

It is a further object of the invention to provide a method forproducing improved electrical connections in high energy igniters.

Other objects and advantages will be apparent from the description whichfollows, reference being had to the accompanying drawings, in which-Fig. 1 is a view in section of a high energy igniter incorporating animproved electrical contact according to the invention; and

Fig. 2 is an enlarged cross-sectional view of a portion of the igniterof Fig. 1 showing a step in the production of the improved electricalconnection according to the invention.

According to the invention an improved high energy igniter is provided.Such igniter comprises a ceramic insulator having a center bore, anelectrically semi-conducting body constituting at least the surface ofthe nose portion of the insulator, a center electrode seated in theUnited States Patent 0 the flange 13 of the shell.

thousandths of an inch separates the electrode 19 from the lower portionof the insulating body 17 and frorit' 23 of the electrode 19 is sealedin the central hole 25 in any known manner as by a suitable sealingmaterial'- insulator bore, and extending adjacent the conductingsurface, a metal shell in which the insulator is seated, a groundelectrode spaced from the center electrode and adjacent the conductingsurface, a metalized coating-in terposed between the center electrodeand the conducting surface, in electrical contact with each, andadhered-to at least one, and a metalized coating interposed between theground electrode and the conducting surface, in electrical contact witheach, and adhered to at least one.

Referring now to the drawings, and particularly to Fig. 1, one specifichigh energy igniter embodying an electrical connection according to the'invention comprises a shell 11 threaded as at 12 for engagement with thewall of the combustion chamber of a jet or reciprocating engine, andprovided, in the constructionshown, with an inwardly extending lowerflange 13. An insulator 15 is-seated and fixed in the shell by acompressed body of holding powder-tamped overa metal sleeve or gasket,and over which is disposed a metallic sleeve 16 threaded into the shell11. The insulator- 15 is composed of an electrically insulating upperportion 17 and an electri-i cally semi-conducting nose portion 18, andsupports a center electrode 19. In assembly, the insulator 15 isdisposed so that the nose portion 18 thereof is seated against a groundelectrode 20, which is in turn the nose portion 18. a The centralelectrode 19 may be of any suitable construction, and in the form shownis composed of aflsterh" part 23 and an integral flange 24. The stempart 23 is received in an enlarged central hole 25 of the insulator" 15,while the flange 24 bears against a flat surface of the nose portion 18of the insulator 15. The stem part 27. A metalized coating 28, which canbe of any -suit-' the insulator 15. A similar metalized coating 29 isinter-' posed between the ground electrode 20 and the nose portion 18 ofthe insulator 15.

- Referring to Fig. 2, the insulator 15 and-semi-conduct-f ing noseportion 18 are shownenlargedwith a metal"- coating 30 applied to theexposed portions of the-body 18. The coating 30 can be a uniformdispersion of colloidal silver in a relatively volatile hydrocarbon oil,preferably a drying oil. Such a dispersion is available commerciallyunder the trade designation DuPont silver 4887. The dispersion can beapplied to the exposed portions of the semi-conducting body 18 bydipping, brushing, spraying, or in any desired manner. The viscosity ofthe dispersion, and with it the thickness of the coating 30, can bevaried by suitable regulation of the ratio of silver, oil and solvent,for example turpentine, in the case of most drying oils. Similardispersions of platinum, gold and copper have also been used, but mostsatisfactory results have been achieved with the silver dispersion.

After the insulator-semi-conducting body assembly (which can beproduced, for example, as described in a co-pending application entitledElectrically Semi-Conducting Body, Serial No. 386,189, filed October 15,1953, by Harry G. Schurecht) has been coated as described in thepreceding paragraph, the electrode 19, which can be silvered in the samemanner, if desired, is inserted in a central bore of the insulator, andthe holding powder 27 tamped in place. The resulting assembly is thenheated to volatilize the oil in the silver or other dispersion, forexample to a temperature from about 1200 Patented Apr. 15,1958

forced against An air gap 21 of a few 3 F. to about'1400 F. forapproximately fifteen minutes.

The electrode-insulator assembly is then locked in the shell 11 as shownin Fig. 1.

After the igniter has been assembled as described the silver or othermetal coating is removed, for example, by mechanical abrasion, from theexposed portions of the insulator, leaving the coating intermediate theground electrode and the conducting body 18, and also intermediate thecenter electrode 19 and the semi-conducting body 18.

It has been found as the result of extensive engine tests that ignitershaving a metalized coating positioned according to the invention havesubstantially increased useful life over identical igniter-s producedwithout such coating, the increase being of the order of 50 to 75percent when the metalizing is with silver, as specifically described.

It will be apparent that various changes and modifications can be madefrom the specific details shown in the attached drawings and discussedin the specification without departing from the spirit of the invention.For example, various metals can be used in place of silver, gold,platinum and copper, previously mentioned specifically, so long as suchmetal does not oxidize or melt at temperatures encountered in service ofan igniter, usually in the vicinity of 1500 F. to 1600 F. Preferably,the metalized coating comprises a metal from group 1(b) of the periodicsystem having an atomic number from 29 through 79, inclusive, i. e.,comprises copper, silver or gold, and most desirably silver or gold. Thehydrocarbon drying oil disclosed specifically acts only as a temporarybinder to hold the finely divided silver particles in place prior tofiring. Other temporary binders, for ex ample a dextrine solution inwater, could be used for this purpose.

While the invention has been described inconnection with a body ofsubstantial size of electrically semi-conducting material along thesurface of which a spark discharge occurs, it is equally operable when asemi-conducting engobe coating having a thickness of, at the most, a fewthousandths of an inch is used in place thereof. In such case it isusually preferred to leave at least a small gap between the portion ofthe coating that will ultimately contact the center electrode and theportion that will contact the ground electrode. The high energy sparkthat occurs across the engobe surface will then vaporize in a short timeany metalized coating that is exposed. If desired, a solvent can be usedto remove the exposed portion of the metalized coating, for exampleafter assembly of the igniter. The final metalized coating in theigniter is present only on portions of the body which are in contactwith the electrodes, the surface of the semi-conducting body along whicha spark discharge occurs not being metalized.

What I claim is:

l. A high energy igniter comprising a ceramic insulator having a centerbore, an electrically semi-conducting body constituting at least thesurface of the nose portion of said insulator, a center electrode seatedin said insulator bore, and extending adjacent said conducting surface,a metal shell in which said insulator is seated, a ground electrodespaced from said center electrode and adjacent said conducting surface,a metalized coating interposed between said center electrode and saidconducting surface, in electrical contact with each, and adhered to atleast one, and a metalized coating interposed between said groundelectrode and said conducting surface, in electrical contact with each,and adhered to at least one.

2. A high energy igniter as claimed in claim 1 in which each of saidmetalized coatings is adhered to said conducting surface.

3. In a high energy igniter including a ceramic insulator having acenter bore, an electrically semi-conducting body constituting at leastthe surface of the nose portion of the insulator, a center electrodeseated in the insulator bore, and extending adjacent the conductingsurface, a

metal shell in which the insulator is seated, and a ground electrodespaced from the center electrode and adjacent the conducting surface,the improvement comprising a metalized coating interposed between thecenter electrode and the conducting surface, in electrical contact witheach, and adhered to at least one, and a metalized coating intei= posedbetween the ground electrode and the conducting surface, in electricalcontact with each, and adhered to at least one.

4. In a high energy igniter, the improvement as claimed in claim 3 inwhich each of said metalized coatings is adhered to the conductingsurface.

5. In a high energy igniter, the improvement as claimed in claim 4 inwhich the metalized surface is composed of a metal from group 1 (b) ofthe periodic system having an atomic number from 29 through 79,inclusive.

References Cited in the file of this patent UNITED STATES PATENTS2,356,053 Hastings et al. Aug. 15, 1944 2,578,754 Smits Dec. 18, 19512,684,665 Tognola July 27, 1954 2,733,369 Smits Jan. 31, 1956 FOREIGNPATENTS 724,211 Great Britain Feb. 16, 1955

